The Influence of Early Adult Experience and Larval Food Restriction on Responses Toward Nonhost Plants in Moths

Experience can induce oviposition on nonhost plants, but little is known about the mechanisms underlying such behavioral changes. In laboratory experiments, we examined the effects of early adult experience of nonhost volatiles and larval food restriction on the olfactory response and oviposition preference of the diamondback moth, Plutella xylostella, a specialist herbivore of cruciferous plants. Naïve ovipositing females showed aversion to the odor of pea, a nonhost plant of P. xylostella, and seldom accepted pea plants for oviposition. However, females with prior experience with pea odor showed preference for the volatiles and significantly increased acceptance of pea plants for oviposition. Larval food restriction did not alter olfactory response and oviposition preference. We conclude that olfactory learning plays a significant role in inducing oviposition on nonhost plants and may contribute to host range expansion in phytophagous insects.     

Modulation of Reproductive Behaviors by Non-Host Volatiles in the Polyphagous Egyptian Cotton Leafworm, Spodoptera littoralis

In order to locate mates, food, and oviposition sites, insects mainly rely on volatile cues released by their sexual partners, food sources, and host and non-host plants. Calling, mating, and oviposition behaviors, as well as fecundity and longevity, of newly emerged Spodoptera littoralis (Bois.) moths were recorded in the presence of volatiles from leaves of a host plant, Gossypium hirsutum (cotton) and two non-host plants, Adhatoda vasica (Av) or Picea abies (spruce), either alone or in host/non-host combinations. Females exposed to cotton volatiles started calling earlier than females exposed to non-host plant volatiles (NHV), or the blank control. Likewise, moth pairs exposed to cotton volatiles started mating earlier than the other treatments. The period of calling in females alone was longer than females kept with males, having the opportunity to mate. However, the callings, as well as mating durations in the moth pairs, in different treatments were not different. Longevity was decreased either in the absence of cotton or the presence of Av, and spruce leaves. Fecundity was reduced in moths exposed to a combination of spruce and cotton. The effect of NHV on attraction of 2-3–day-old male moths towards a pheromone (Ph) source was studied in a wind tunnel. In the no-choice assay, more males arrived at close approach and landed on the Ph source when the host plant, cotton, was offered in the background as compared to the non-hosts. In the dual-choice assay, more males landed on the Ph source in front of the host plant compared to the Ph source in front of non-hosts. Gas chromatography-electroantennographic detection on female S. littoralis revealed five antennally active compounds in headspace collections of spruce and three compounds in Av.     

Mating Disruption of a Carpenter Moth, <Emphasis Type="Italic">Cossus insularis</Emphasis> (Lepidoptera: Cossidae) in Apple Orchards with Synthetic Sex Pheromone,and Registration of the Pheromone as an Agrochemical

Mating disruption of the carpenter moth, Cossus insularis (Staudinger) (Lepidoptera: Cossidae), with a synthetic version of its sex pheromone, a mixture of (E)-3-tetradecenyl acetate and (Z)-3-tetradecenyl acetate, was tested for three successive years in apple (Malus domestica Borkh.) orchards. Pheromone trap catches, percentage mating of tethered females and females enclosed with males in a mating cage, and tree damage were measured in both the pheromone-treated and untreated control orchards. The attraction of male moths to pheromone traps at heights of 1.5, 3, and 5 m was strongly disrupted when the pheromone dispensers were placed at 1.5 m height. Mating of tethered females placed at 1 m was completely inhibited, and the mating of tethered females at a height of 3 m was significantly reduced by the treatment in comparison to matings in an untreated control orchard. Similarly, mating of pairs of moths enclosed in mating cages was significantly reduced by the synthetic pheromone treatment in comparison to controls. The percentage of damaged trees in the pheromone-treated orchard also decreased significantly over the course of the experiment. These results suggest that mating disruption with the synthetic sex pheromone appears promising for reducing damage caused by C. insularis in apple orchards in Japan, and a commercial mating disruption product has been developed and registered.     

Enhancement of Attraction to Sex Pheromones of Spodoptera exigua by Volatile Compounds Produced by Host Plants

We measured the effects of exposure to volatile compounds produced by host plants on the rate of capture of male Spodoptera exigua using synthetic sex pheromones. Exposure to volatile compounds stimulated strong electroantennographic responses of male S. exigua. The behavioral responses of male moths to combinations of sex pheromone and volatile compounds were tested in wind tunnel experiments. When lures were baited with synthetic sex pheromone plus benzaldehyde, phenylacetaldehyde, (Z)-3-hexenyl acetate, or linalool, respectively, the landing rate of S. exigua males was increased by 101.4%, 79.6%, 60.6%, and 34.3%, respectively, compared to sex pheromone alone. In field tests, traps baited with either pheromone + (E)-2-hexenal, pheromone + phenylacetaldehyde, pheromone + (Z)-3-hexenyl acetate, or pheromone + (Z)-3-hexenol enhanced moth catches by 38.8%, 34.6%, 24.6%, and 20.8%, respectively compared to traps baited with pheromone alone. In a second field experiment, more S. exigua males were trapped with a combination of a synthetic sex pheromone blend and several individual host plant volatiles compared to synthetic sex pheromone alone. These results suggest that some host plant volatiles enhance the orientation response of S. exigua male moths to sex pheromone sources.     

RNAi-Induced Electrophysiological and Behavioral Changes Reveal two Pheromone Binding Proteins of <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> Involved in the Perception of the Main Sex Pheromone Component <Emphasis Type="Italic">Z</Emphasis>11–16:Ald

Pheromone binding proteins (PBPs) are thought to play key roles in insect sex pheromone recognition; however, there is little in vivo evidence to support this viewpoint in comparison to abundant biochemical data in vitro. In the present study, two noctuid PBP genes HarmPBP1 and HarmPBP2 of the serious agricultural pest, Helicoverpa armigera were selected to be knocked down by RNA interference, and then the changes in electrophysiological and behavioral responses of male mutants to their major sex pheromone component (Z)-11-hexadecenal (Z11–16:Ald) were recorded. There were no significant electrophysiological or behavioral changes of tested male moths in response to Z11–16:Ald when either single PBP gene was knocked down. However, decreased sensitivity of male moths in response to Z11–16:Ald was observed when both HarmPBP1 and HarmPBP2 genes were silenced. These results reveal that both HarmPBP1 and HarmPBP2 are required for the recognition of the main sex pheromone component Z11–16:Ald in H. armigera. Furthermore, these findings may help clarify physiological roles of moth PBPs in the sex pheromone recognition pathway, which in turn could facilitate pest control by exploring sex pheromone blocking agents.     

“This is not an Apple”–Yeast Mutualism in Codling Moth

The larva of codling moth Cydia pomonella (Tortricidae, Lepidoptera) is known as the worm in the apple, mining the fruit for food. We here show that codling moth larvae are closely associated with yeasts of the genus Metschnikowia. Yeast is an essential part of the larval diet and further promotes larval survival by reducing the incidence of fungal infestations in the apple. Larval feeding, on the other hand, enables yeast proliferation on unripe fruit. Chemical, physiological and behavioral analyses demonstrate that codling moth senses and responds to yeast aroma. Female moths are attracted to fermenting yeast and lay more eggs on yeast-inoculated than on yeast-free apples. An olfactory response to yeast volatiles strongly suggests a contributing role of yeast in host finding, in addition to plant volatiles. Codling moth is a widely studied insect of worldwide economic importance, and it is noteworthy that its association with yeasts has gone unnoticed. Tripartite relationships between moths, plants, and microorganisms may, accordingly, be more widespread than previously thought. It, therefore, is important to study the impact of microorganisms on host plant ecology and their contribution to the signals that mediate host plant finding and recognition. A better comprehension of host volatile signatures also will facilitate further development of semiochemicals for sustainable insect control.     

Single-Component Pheromone Consisting of Bombykal in a Diurnal Hawk Moth, <Emphasis Type="Italic">Neogurelca himachala sangaica</Emphasis>

Recent work has suggested that hawk moths share pheromone components but are sexually separated by qualitative and quantitative differences in their pheromone blends. During field assays on the sex pheromones of other species, a diurnal hawk moth, Neogurelca himachala sangaica (Lepidoptera: Sphingidae), was frequently captured, but the composition of the sex pheromone of this species was not known. Analysis of hexane extracts of the pheromone glands of calling female by gas chromatography (GC) using an electroantennographic detector (EAD) revealed two components that elicited EAD responses from male moth antennae. These components were identified by their mass spectra and retention indices on two GC columns as (10E,12Z)-10,12-hexadecadienal (E10,Z12–16:Ald) and a trace of its (10E,12E)-isomer (E10,E12–16:Ald) in 98:2 ratio. In field experiments, E10,Z12–16:Ald alone attracted male moths, and addition of E10,E12–16:Ald significantly reduced the attractiveness, even at the naturally-occurring ratio. Analysis of the data using a generalized linear mixed model showed that E10,Z12–16:Ald positively contributed to attractiveness, whereas E10,E12–16:Ald did so negatively, and it was concluded that the sex pheromone of N. himachala sangaica consists solely of E10,Z12–16:Ald, bombykal. The negative effect of E10,E12–16:Ald on attractiveness could promote the species-specificity of this single-component pheromone system.     

Kairomonal Response of the Parasitoid, <Emphasis Type="Italic">Bracon hebetor</Emphasis> Say,to the Male-Produced Sex Pheromone of Its Host,the Greater Waxmoth, <Emphasis Type="Italic">Galleria mellonella</Emphasis> (L.)

Bracon hebetor is a larval ectoparasitoid that utilizes several pests belonging to the family Pyralidae (Lepidoptera) as hosts. In the present study, we analyzed the kairomonal response of this wasp to the male-produced sex pheromone of a host, the greater wax moth Galleria mellonella, an economically important pest of honeybees, Apis mellifera. Coupled gas chromatography-electroantennographic detection (GC-EAD) revealed three compounds in headspace collections from male G. mellonella that elicited responses from B. hebetor antennae: decanal and the previously identified sex pheromone components, nonanal and undecanal. Y-tube olfactometer tests that used naïve, mated wasps showed that females, but not males, were highly attracted to (a) male G. mellonella headspace samples, (b) two synthetic blends of nonanal and undecanal (in ratios matching that found in male moth samples), and (c) the two aldehydes tested individually. Further, female wasps did not discriminate between a blend of aldehydes and male G. mellonella headspace. In dose-response trials that used octanal, nonanal, decanal, and undecanal, no difference in EAG responses of the two sexes was observed, except for undecanal at the second highest dose, for which female antennae showed significantly larger responses than did male antennae. When the two binary blends were tested at different doses, female wasps were significantly attracted to the two highest doses (1 µg and 10 µg), but not to the lowest dose (100 ng). Our results show that females of this economically important parasitoid utilize the male-produced sex pheromone of a host as an indirect cue to guide them to potential oviposition sites.     

Antennal responses of the two host races of the larch bud moth,Zeiraphera diniana,to larch and cembran pine volatiles

The larch bud moth (LBM) Zeiraphera diniana Guenée causes defoliation on larch in the Alps at 8- to 10-year intervals, after which populations crash. There are two LBM host races, one on larch and the other on cembran pine. These host races are morphologically indistinguishable as adults but they differ genetically in larval color types. Furthermore, females of each host race produce distinct pheromone blends and show oviposition preferences for their respective hosts. It is not clear to what extent host choice contributes to assortative mating in the LBM. Here, we compare the olfactory sensitivities of the two host races to the odors of fresh foliage of the host plants using the electroantennogram (EAG) technique, and the responses of the two host races to volatiles collected from the two host plants as analyzed by gas-chromatography-linked antennographic detection (GC-EAD). Both sexes of the larch and cembran host races show the same EAG responses to vapors of fresh larch and cembran pine foliage. Fifteen plant volatiles identified as chemostimuli by GC-EAD from larch and cembran pine odors elicited the same antennogram responses from the two host races. However, the GC-EAD analyses indicate that the number and quantity of chemostimuli emanating from each host plant is different. It is, therefore, most probably the array of olfactory receptors responding to the bouquet of volatiles unique to each host plant that underlies the host preferences of the two races. What remains open is the extent to which the similarity of the olfactory systems may contribute to cross-attraction. The fact that LBM individuals with intermediate characteristics between the two host races exist, suggests that olfactory perception does not hinder gene flow and contributes to sustained genetic diversity within the species Z. diniana.     

Host Plant Species Differentiation in a Polyphagous Moth: Olfaction is Enough

Polyphagous herbivorous insects need to discriminate suitable from unsuitable host plants in complex plant communities. While studies on the olfactory system of monophagous herbivores have revealed close adaptations to their host plant’s characteristic volatiles, such adaptive fine-tuning is not possible when a large diversity of plants is suitable. Instead, the available literature on polyphagous herbivore preferences suggests a higher level of plasticity, and a bias towards previously experienced plant species. It is therefore necessary to take into account the diversity of plant odors that polyphagous herbivores encounter in the wild in order to unravel the olfactory basis of their host plant choice behaviour. In this study we show that a polyphagous moth, Spodoptera littoralis, has the sensory ability to distinguish five host plant species using olfaction alone, this being a prerequisite to the ability to make a choice. We have used gas chromatography mass spectrometry (GC-MS) and gas chromatography electroantennographic detection (GC-EAD) in order to describe host plant odor profiles as perceived by S. littoralis. We find that each plant emits specific combinations and proportions of GC-EAD active volatiles, leading to statistically distinct profiles. In addition, at least four of these plants show GC-EAD active compound proportions that are conserved across individual plants, a characteristic that enables insects to act upon previous olfactory experiences during host plant choice. By identifying the volatiles involved in olfactory differentiation of alternative host plants by Spodoptera littoralis, we set the groundwork for deeper investigations of how olfactory perceptions translate into behaviour in polyphagous herbivores.     

Sex Attractant Pheromone of the Luna Moth, <Emphasis Type="Italic">Actias luna</Emphasis> (Linnaeus)

Giant silk moths (Lepidoptera: Saturniidae) typically are not well represented as larvae or adults in community level inventories of Lepidoptera, and as a result, little is known about their population dynamics. Furthermore, in recent years, many species of silk moths appear to have experienced population declines. Volatile sex pheromones are powerful sampling tools that can be used in operational conservation and monitoring programs for insects. Here, we describe the identification of the sex attractant pheromone of a giant silk moth, the luna moth Actias luna. Coupled gas chromatography-electroantennographic detection and gas chromatography-mass spectrometric analyses of extracts from pheromone glands of female luna moths supported the identification of (6E,11Z)-6,11-octadecadienal (E6,Z11–18:Ald), (6E)-6-octadecenal (E6–18:Ald), and (11Z)-11-octadecenal (Z11–18:Ald) as the compounds in extracts that elicited responses from antennae of male moths. These identifications were confirmed by synthesis, followed by testing of blends of the synthetic compounds in field trials in Ontario, Canada, and Kentucky, USA. Male moths were attracted to synthetic E6,Z11–18:Ald as a single component. Attraction appeared to be enhanced by addition of E6–18:Ald but not Z11–18:Ald, suggesting that the luna moth pheromone consists of a blend of E6,Z11–18:Ald and E6–18:Ald.     

Exploring the Effects of Plant Odors,from Tree Species of Differing Host Quality,on the Response of <Emphasis Type="Italic">Lymantria dispar</Emphasis> Males to Female Sex Pheromones

A widely accepted hypothesis for host-plant selection in herbivorous insects is that ovipositing females select host-plants that maximize the survival and performance of their offspring. However, numerous studies indicate that this is not always the case for polyphagous species. Lymantria dispar is a highly polyphagous forest defoliator and has flightless females in some subspecies, resulting in a limited capacity to make host-choices. Males of other Lepidopteran species utilize a combination of sexual pheromones and plant volatiles in their mating choices and exhibit preferences among plant species. We explored the behavior of L. dispar males towards sexual pheromone in the presence and absence of plant volatiles and their ability to discriminate between two plant species with different degrees of suitability for their offspring: a suboptimal host (Pinus sylvestris), and an optimal host (Quercus robur). In no-choice wind tunnel assays, we found that rates of male success in locating a pheromone source were not altered by the presence of plant odors; however, the time spent by males searching for the pheromone source after reaching the full length of the tunnel was reduced by more than 50% in the presence of plant volatiles. In dual choice assays, males exhibited a clear preference for a combination of pheromones and plant volatiles over the pheromone alone. However, we did not find evidence of an innate ability to discriminate between the odors of optimal and suboptimal host plants. We discuss possible ecological and evolutionary explanations for these observations.     

Plant Volatiles Enhance Behavioral Responses of Grapevine Moth Males, Lobesia botrana to Sex Pheromone

Plant volatiles play an important role in the lives of phytophagous insects, by guiding them to oviposition, feeding and mating sites. We tested the effects of different host-plant volatiles on attraction of Lobesia botrana males to the female-produced sex pheromone, in a wind tunnel. Addition of volatile emissions from grapevines or individual plant volatiles to pheromone increased the behavioral responses of L. botrana males over those to pheromone alone. At a low release rate (under-dosed) of pheromone, addition of (E)-β-caryophyllene, (Z)-3-hexenyl acetate, 1-hexanol, or 1-octen-3-ol increased all behavioral responses, from activation to pheromone source contact, while addition of (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-β-farnesene, (Z)-3-hexenol, or methyl salicylate affected only the initial behavioral responses. Dose–response experiments suggested an optimal release ratio of 1:1000 (sex pheromone: host plant volatile). Our results highlight the role of plant volatiles in the sensory ecology of L. botrana.     

Mating Disruption as a Suppression Tactic in Programs Targeting Regulated Lepidopteran Pests in US

Mating disruption, the broadcast application of sex-attractant pheromone to reduce the ability of insects to locate mates, has proven to be an effective method for suppressing populations of numerous moth pests. Since the conception of mating disruption, the species-specificity and low toxicity of pheromone applications has led to their consideration for use in area-wide programs to manage invasive moths. Case histories are presented for four such programs where the tactic was used in the United States: Pectinophora gossypiella (pink bollworm), Lymantria dispar (gypsy moth), Epiphyas postvittana (light brown apple moth), and Lobesia botrana (European grapevine moth). Use of mating disruption against P. gossypiella and L. botrana was restricted primarily to agricultural areas and relied in part (P. gossypiella) or wholly (L. botrana) on hand-applied dispensers. In those programs, mating disruption was integrated with other suppression tactics and considered an important component of overall efforts that are leading toward eradication of the invasive pests from North America. By contrast, L. dispar and E. postvittana are polyphagous pests, where pheromone formulations have been applied aerially as stand-alone treatments across broad areas, including residential neighborhoods. For L. dispar, mating disruption has been a key component in the program to slow the spread of the infestation of this pest, and the applications generally have been well tolerated by the public. For E. postvittana, public outcry halted the use of aerially applied mating disruption after an initial series of treatments, effectively thwarting an attempt to eradicate this pest from California. Reasons for the discrepancies between these two programs are not entirely clear.     

Identification of Host Fruit Volatiles from Snowberry (<Emphasis Type="Italic">Symphoricarpos albus</Emphasis>), Attractive to <Emphasis Type="Italic">Rhagoletis zephyria</Emphasis> Flies from the Western United States

A mixture of behaviorally active volatiles was identified from the fruit of snowberry, Symphoricarpos albus laevigatus, for Rhagoletis zephyria flies reared from snowberry fruit. A nine-component blend containing 3-methylbutan-1-ol (3%), dimethyl trisulfide (1%), 1-octen-3-ol (40%), myrcene (8%), nonanal (9%), linalool (13%), (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT, 6%), decanal (15%), and β-caryophyllene (5%) was identified that gave consistent electroantennogram activity and was behaviorally active in flight tunnel tests. In other flight tunnel assays, snowberry flies from two sites in Washington state, USA, displayed significantly greater levels of upwind oriented flight to sources with the snowberry volatile blend compared with previously identified volatile blends from domestic apple (Malus domestica) and downy hawthorn (Crataegus mollis) fruit from the eastern USA, and domestic apple, black hawthorn (C. douglasii) and ornamental hawthorn (C. monogyna) from Washington state. Selected subtraction assays showed that whereas removal of DMNT or 1-octen-3-ol significantly reduced the level of upwind flight, removal of myrcene and β-caryophyllene, or dimethyl trisulfide alone did not significantly affect the proportion of upwind flights. Our findings add to previous studies showing that populations of Rhagoletis flies infesting different host fruit are attracted to unique mixtures of volatile compounds specific to their respective host plants. Taken together, the results support the hypothesis that differences among flies in their behavioral responses to host fruit odors represent key adaptations involved in sympatric host plant shifts, contributing to host specific mating and generating prezygotic reproductive isolation among members of the R. pomonella sibling species complex.     

Regulatory Innovation,Mating Disruption and 4-Play<Superscript>TM</Superscript> in New Zealand

Straight-chained lepidopteran pheromones are now regulated under a group standard in New Zealand, which is generic for moth pheromone products of similar low risk, under the Hazardous Substances and New Organisms Act (1996). This means that compliant new pheromone products can be developed and commercialized with low regulatory requirements. This encourages innovation and supports fruit industries interested in meeting export phytosanitary standards, while targeting low or nil residues of pesticides. Changes to pheromone blends for reasons such as technical improvements or variations in pest species composition in different crops can be made with minimal regulatory involvement. We illustrate how this system now operates with a four species mating disruption product commercialized in 2012. The odors involved in “4-Play?” consist of a range of components used by codling moth (Cydia pomonella), lightbrown apple moth (Epiphyas postvittana), green-headed leafroller (Planotortrix octo), and brown-headed leafroller (Ctenopseustis obliquana). The development of 4-Play? illustrates how mating disruption of insects can support industry goals.     

Plant Volatiles Increase Sex Pheromone Attraction of <Emphasis Type="Italic">Holotrichia parallela</Emphasis> (Coleoptera: Scarabaeoidea)

Holotrichia parallela (Coleoptera: Scarabaeoidea) is a notorious pest of many crops. To improve the effectiveness of its female-produced sex pheromone (L-isoleucine methyl ester:(R)-(?)-linalool = 6:1), 14 plant volatiles, including dodecanoic acid, dodecanal, farnesol, α-farnesene, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, (Z)-3-hexenyl acetate, (E)-2-hexenyl acetate, (R)-(+)-limonene, α-phellandrene, α-pinene, ocimene, methyl benzoate, and benzaldehyde, were individually evaluated using electroantennography and olfactometer assays. (E)-2-Hexenyl acetate and (Z)-3-hexenyl acetate were found to elicit the strongest responses in both males and females. Further testing of these two compounds in mixtures with the sex pheromone indicated that (E)-2-hexenyl acetate had a stronger synergistic effect than (Z)-3-hexenyl acetate. Field evaluations showed that mixtures of (E)-2-hexenyl acetate and the sex pheromone resulted in significantly higher catches than the sex pheromone alone. Using a 5:1 mixture of the sex pheromone and (E)-2-hexenyl acetate, the maximum number of females per trap per day was 14, showing a synergistic effect of a factor of four. For males, a 3:1 mixture of the sex pheromone and (E)-2-hexenyl acetate yielded a maximum number of 310 individuals per trap per day, equivalent to a synergistic effect of 175%. These results may provide the basis for the development of efficient pest management systems against H. parallela using plant volatiles and insect sex pheromones.     

Experience-Induced Habituation and Preference Towards Non-Host Plant Odors in Ovipositing Females of a Moth

In phytophagous insects, experience can increase positive responses towards non-host plant extracts or induce oviposition on non-host plants, but the underlying chemical and behavioral mechanisms are poorly understood. By using the diamondback moth, Plutella xylostella, its host plant Chinese cabbage, and a non-host plant Chrysanthemum morifolium, as a model system, we observed the experience-altered olfactory responses of ovipositing females towards volatiles of the non-host plant, volatiles of pure chemicals (p-cymene and α-terpinene) found in the non-host plant, and volatiles of host plants treated with these chemicals. We assessed the experience-altered oviposition preference towards host plants treated with p-cymene. Naive females showed aversion to the odors of the non-host plant, the pure chemicals, and the pure chemical-treated host plants. In contrast, experienced females either became attracted by these non-host odors or were no longer repelled by these odors. Similarly, naive females laid a significantly lower proportion of eggs on pure chemical-treated host plants than on untreated host plants, but experienced females laid a similar or higher proportion of eggs on pure chemical-treated host plants compared to untreated host plants. Chemical analysis indicated that application of the non-host pure chemicals on Chinese cabbage induced emissions of volatiles by this host plant. We conclude that induced preference for previously repellent compounds is a major mechanism that leads to behavioral changes of this moth towards non-host plants or their extracts.     

Reduced Mating Success of Female Tortricid Moths Following Intense Pheromone Auto-Exposure Varies with Sophistication of Mating System

Mating disruption is a valuable tool for the management of pest lepidopteran species in many agricultural crops. Many studies have addressed the effect of female pheromone on the ability of males to find calling females but, so far, fewer have addressed the effect of pheromone on the mating behavior of females. We hypothesized that mating of female moth species may be adversely affected following sex pheromone auto-exposure, due to abnormal behavioral activity and/or antennal sensitivity. Our results indicate that, for Grapholita molesta and Pandemis pyrusana females, copulation, but not calling, was reduced following pre-exposure to sex pheromone. In contrast, for Cydia pomonella and Choristoneura rosaceana, sex pheromone pre-exposure did not affect either calling or copulation propensity. Adaptation of female moth antennae to their own sex pheromone, following sex pheromone auto-exposure, as measured by electroantennograms, occurred in a species for which identical exposure reduced mating success (G. molesta) and in a species for which such exposure did not affect mating success (C. rosaceana). These results suggest that pre-exposure of female moths of certain species to sex pheromone may further contribute to the success of pheromone-based mating disruption. Therefore, we conclude that, in some species, mating disruption may include a secondary mechanism that affects the mating behavior of female moths, in addition to that of males.     

Responses of Parasitoids to Volatiles Induced by <Emphasis Type="Italic">Chilo partellus</Emphasis> Oviposition on Teosinte,a Wild Ancestor of Maize

Maize, a genetically diverse crop, is the domesticated descendent of its wild ancestor, teosinte. Recently, we have shown that certain maize landraces possess a valuable indirect defense trait not present in commercial hybrids. Plants of these landraces release herbivore-induced plant volatiles (HIPVs) that attract both egg [Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)] and larval [Cotesia sesamiae Cameron (Hymenoptera: Braconidae)] parasitoids in response to stemborer egg deposition. In this study, we tested whether this trait also exists in the germplasm of wild Zea species. Headspace samples were collected from plants exposed to egg deposition by Chilo partellus Swinhoe (Lepidoptera: Crambidae) moths and unexposed control plants. Four-arm olfactometer bioassays with parasitic wasps, T. bournieri and C. sesamiae, indicated that both egg and larval parasitoids preferred HIPVs from plants with eggs in four of the five teosinte species sampled. Headspace samples from oviposited plants released higher amounts of EAG-active compounds such as (E)-4,8-dimethyl-1,3,7-nonatriene. In oviposition choice bioassays, plants without eggs were significantly preferred for subsequent oviposition by moths compared to plants with prior oviposition. These results suggest that this induced indirect defence trait is not limited to landraces but occurs in wild Zea species and appears to be an ancestral trait. Hence, these species possess a valuable trait that could be introgressed into domesticated maize lines to provide indirect defense mechanisms against stemborers.